Method of Making Medium Density Fiberboard

ABSTRACT

The present invention provides a method for producing an MDF board from pulp from a fibrous lignocellulose material using a treatment or pretreatment step which exposes the material to oxalic acid or oxalic acid derivatives (particularly dialkyl ester derivatives, particularly in the vapor phase). The treated wood is then subjected to a sugar extraction wash and refined using any one of the several pulping methods to produce a final pulp product. Once this is done the pulp is used to make MDF boards having improved water repellency properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/824,383 filed on Sep. 1, 2006

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States government support awarded bythe following agency: DOE Grant # R530539 and DOA # DE-FG45-02R530539.The United States has certain rights in this invention.

BACKGROUND OF THE INVENTION

Lignocellulosic materials are sources for the generation of a variety ofproducts. Some of the products retain significant structural componentsof the lignocellulose such as mechanical pulp Fibers from wood chips.Other compounds such as sugars derived from the carbohydrate inlignocellulose are made into products by fermentation or chemicalconversion. The lignocellulose can be made into products that representa continuum of structured to molecular products. The continuum ofproducts is generated by a variety of physical, chemical, biological andthermal processes.

Medium-density fiberboard (MDF) is an engineered wood product formed bylignocellulosic fibers glued under heat, pressure and a small amount ofresin. In manufacturing MDF from wood, the wood is first reduced to anintermediate stage in which the fibers in the wood are separated fromtheir natural environment and transformed into a pulp like suspension.One of the components of wood is lignocellulose. The most abundantcomponent of lignocellulose is the cellulose polymers. These are themost desired polymers in the final product. The second most abundantpolymer is lignin. Lignin is useful as a material which allows fibers toadhere in MDF.

The third major component of lignocellulose is the hemicellulose.Hemicelluloses are polymers of sugars that are more heterogeneous thancellulose. The hemicelluloses are comprised of oligomeric sugars derivedfrom arabinose, galactose, xylose and mannose in addition to glucose.The hemicellulose and the lignin are intermixed with the cellulose inlignocellulose and serve to protect the cellulose from damage byorganisms, enzymes or chemicals. Removal of the hemicellulose and ligninis often a portion of lignocellulose processing.

Pulp suitable for MDF production may be produced from various types oflignocellulose using any one of several techniques. The simplest ofthese techniques is the refiner mechanical pulping (RMP) method in whicha mechanical milling operation grinds or abrades wood in water until adesired state of freeness (an arbitrary measure of water drainage) isachieved between its fibers. The RMP method is high yield, typicallyconverting approximately 95% of the dry weight of the wood into pulp.The RMP method leaves most of the lignin and hemicellulose in the pulp.

Other mechanical pulping methodologies include thermo-mechanical pulping(TMP), chemical treatment with thermo-mechanical pulping (CTMP), andchemi-mechanical pulping (CMP). Alternatively there are also chemicalpulping methods, wherein a chemical/water solution is generally used todissolve the lignin and hemicellulose to promote the separation of thefibers.

In thermo-mechanical processes (e.g. TMP and CTMP), high temperaturesare used to help separate the fibers during refining. These processesgenerally require the refining to be carried out in one or more steps.The first step is usually a pressurized step with refining beingperformed at temperatures above 100° C. and immediately below or at thesoftening temperature of lignin. During this step, the pulp is typicallymechanically processed using the TMP method. In subsequent steps, thepressure and temperature is usually modulated to achieve the desiredstate of freeness between the fibers.

Relatively high total electric energy amounts or high quantities ofinput lignocellulose are required to produce pulps using the abovementioned mechanical pulping techniques. In particular, high energyinputs are generally required to obtain fiber separation in woods richin lignin as such woods typically call for extended refining periods andhigher refining temperatures or pressures. Recent studies have alsosuggested that even thermal or chemical softening treatments of suchwoods do not guarantee a lower total energy consumption. This is becauseunprocessed fibers which are only mildly separated by the thermal orchemical treatments are difficult to fibrillate during the mechanicalrefining process.

Fibrillation is necessary to increase the flexibility of the fibers andbring about the fine material characteristics of quality processed pulp.In fact, it has been suggested that a decrease in the energy consumptionfrom an established level in various TMP and CTMP processes has beenassociated with the deterioration of certain pulp properties, includinga reduction in the long fiber content of the pulp (See U.S. Pat. No.5,853,534, which is incorporated by reference here in its entirety). Asa result, high energy consumption in TMP and CTMP processes has beengenerally necessary in today's pulping practices.

Along with the problems of the high energy cost of pulping. MDF has theproblem of generally having low moisture tolerance. MDF, therefore,often swells when contacted with water and is therefore of more limiteduse in outdoor settings and in applications that encounter moisture suchas furniture surfaces. Absorption of moisture also often causessignificant deterioration in the mechanical integrity of the MDF.

In regards to reducing the energy costs of pulping, applicants inventeda method for producing pulp from fibrous lignocellulose material using atreatment step which exposes the material to oxalic acid, or oxalic acidand sodium bisulfite, prior to pulping. Applicants discovered thatpulping the resulting product actually required less energy input andprovided a pulp with enhanced physical properties as compared tountreated fibrous lignocellulose material (see, U.S. Patent PublicationNo. 20030041985). From this applicants determined that pretreatment withoxalic acid or oxalic acid derivatives reduced energy requirements inmechanical refining for making paper. This technology is different fromthat which is described hereinbelow for MDF, as the properties of fibersrelevant to making paper sheets are specific to paper products and arenot related to the properties that fibers will exhibit when formed intoMDF. In particular, the methods described below produce MDF that has,in-part, improved water repellency, a resulting characteristic that isnot observable in the papermaking process.

Accordingly, an improved method is needed for producing pulp which isenergy efficient and is able to produce MDF having improved waterrepellency properties.

SUMMARY OF THE INVENTION

Briefly, in one aspect, the present invention is a novel method forproducing an MDF board from pulp from a fibrous lignocellulose materialusing a treatment or pretreatment step which exposes the material tooxalic acid or oxalic acid derivatives (particularly dialkyl esterderivatives, particularly in the vapor phase). The treated wood is thensubjected to a sugar extraction wash and refined using any one of theseveral pulping methods to produce a final pulp product. Once this isdone the pulp is used to make MDF boards having improved waterrepellency properties.

In one embodiment, the method includes heating the fibrouslignocellulose material (without reducing the material to a specificparticle size) at a temperature of between about 90° C. and 170° C.,more suitably between 130° C. and 140° C. in the presence of oxalic acidor oxalic acid derivatives (optionally in the vapor phase), prior torefining the material into a pulp. The dry weight amount of oxalic acidor oxalic acid derivative employed may be less than about 6%, orsuitably less than about 5%, or more suitably between about 0.05% and5%, or most suitably between about 1% and 3%, of the dry weight of thefibrous lignocellulose material. The treatment may be conducted atambient pressures or higher, and for a period of time sufficient toallow the treated product to be later refined at reduced energy inputlevels as compared to untreated materials, typically less than about 4hours.

Another aspect of the invention is a method of making medium densityfiberboard having improved moisture tolerance comprising the steps oracts of providing a reduced material in water comprising one or morefibrous lignocelluloses having particle sizes in the range of 1-100 mmin length, treating the reduced material with a compound having theformula

wherein R₁ and R₂ are independently a member selected from the groupconsisting of —OH, halide, substituted amine, unsubstituted amine, —OR₃,and

wherein R₃ and R₄ are independently a branched or unbranched, cyclic orlinear, saturated or unsaturated, substituted or unsubstituted C₁-C₁₀alkyl, at a temperature in the range of 90-170° C. generating a treatedreduced material, extracting hemicellulose sugars from the treatedreduced material before or after refining it to a pulp, adding asuitable resin to the fibrous pulp, and forming the fibrous pulp intomedium density fiber board. In an alternative embodiment, the compoundincludes the proviso that at least one of R₁ and R₂ is other than —OH.

In an exemplary embodiment of the method, the reduced material istreated with less than 6 dry wt % of the compound.

In another exemplary embodiment of the method, the reduced material istreated with 0.05-5 dry wt % of the compound.

In another exemplary embodiment of the method, the reduced material istreated with 1-3 dry wt % of the compound.

In another exemplary embodiment of the method, R₁ and R₂ are —OH.

In another exemplary embodiment of the method, R₁ and R₂ are —OR₃, andR₃ is an ethyl.

In another exemplary embodiment of the method, R₁ and R₂ are —OR₃, andR₃ is a methyl.

In another exemplary embodiment of the method, the reduced material istreated at a pressure less than 90 psig.

In another exemplary embodiment of the method, the reduced material istreated for a duration less than 4 hours.

In another exemplary embodiment of the method, the reduced material istreated for a duration in the range of 5 min. to 2 hours.

In another exemplary embodiment of the method, the reduced material istreated at a temperature in the range of 130-140° C.

In another exemplary embodiment of the method, the suitable resin is aphenol-formaldehyde resin, and a wax is further added to the fibrouspulp.

In another exemplary embodiment of the method, the medium density fiberboard comprises 93.5 wt % fiber, 6 wt % resin, and 0.5% wax.

In another exemplary embodiment of the method, the reduced material isprovided by using a processing technique being mechanical pulping,thermo-mechanical pulping, or chemical treatment with mechanicalpulping.

In another exemplary embodiment of the method, the method furtherincludes the steps or acts of mechanically refining the treated reducedmaterial one or more times to achieve a predetermined level of freenessof the treated reduced material, and, dewatering the refined and treatedreduced material one or more times. The treated reduced material may bemechanically refined 2-6 times, whereby a freeness value of 100 ml CSF(Canadian Standard Freeness) is achieved.

In another exemplary embodiment of the method, the ratio ofwater:fibrous lignocellulose is in the range of 4:1 to 8:1.

In another exemplary embodiment of the method, the fibrouslignocellulose includes one or more hardwoods or softwoods, such assouthern yellow pine, red pine, spruce, western hemlock, aspen, loblollypine and recovered paper.

In another exemplary embodiment of the method, the particle size is inthe range of 6-14 mm in length.

In another exemplary embodiment of the method, the reduced material isfurther treated with one or more suitable enzymes and/or acetic acid.

Another aspect of the invention is a medium density fiber board made byany one of the methods set forth herein.

Before the embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangements of the components setforth in the following description. The invention is capable of otherembodiments and of being practiced or being carried out in various ways.Also, it is understood that the phraseology and terminology used hereinare for the purpose of description and should not be regarded aslimiting. The use of “including”, “having” and “comprising” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items andequivalents thereof.

It also is understood that any numerical value recited herein includesall values from the lower value to the upper value. For example, if atemperature range is stated as 100° C. to 170° C., it is intended thatvalues such as 101° C. to 110° C., 102° C. to 105° C., etc., areexpressly enumerated in this specification. These are only examples ofwhat is specifically intended, and all possible combinations ofnumerical values between the lowest value and the highest valueenumerated are to be considered to be expressly stated in thisapplication.

Other objects, advantages and features of the present invention willbecome apparent from the following specification and claims.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention is a method for treating lignocellulosic materialsso as to produce pulp which is used to make MDF boards. The presentinvention comprises a pretreatment step which exposes the material tooxalic acid or oxalic acid derivatives. In general, the step includesheat treating the fibrous lignocellulosic material (e.g., wood) incombination with oxalic acid or oxalic acid derivatives. The treatedfibrous material is then refined using any one of several pulpingmethods to produce a pulp product. The treated material is subjected toa sugar extraction process before or after refining, and the releasedsugars may be recovered for other products.

The treatment method of the invention removes hemicellulose from bothhardwoods and softwoods. Since the method releases hemicellulosic sugarsit can be used in systems where hemicellulose is present and might beavailable for recovery and may or may not have to be removed to createanother product from the material. Thus hardwood, softwood chips andbark could be used as well as pulp products and agricultural residues.The treatment of lignocellulosic materials by this process provides ahemicellulosic hydrolysate directly, but the saccharification oflignocellulose to sugars can further be enhanced by enzymes or furtheracid hydrolysis. The method also provides electrical energy savings inthe production of pulp. The subsequent pulp is used to produce MDFboards having improved water repellency characteristics.

Fibrous lignocellulosic materials treated in accordance with the presentinvention are defined to generally include materials containingcellulose polymers, hemicellulose polymers and lignin. Such materialsmay include, for example, hardwoods (i.e., broad-leafed species) andsoftwoods (i.e., conifers). More specifically, these materials mayinclude the Southern Yellow Pines, Spruces, Western Hemlock, Aspens, andother smaller diameter trees. The material may also originate fromeither round wood (e.g., whole trees), residue (e.g., wood scraps leftbehind from forest and sawmill operations), or recovered paper.Recovered paper may include both pre-consumer recovered paper, such astrimmings and scraps from printing, carton manufacturing, or otherconverting processes which are reused to make pulp without reaching thefinal consumer, or post-consumer paper, such as corrugated boxes,newspapers, magazines, and office paper which has been recycled.

Oxalic acid derivative or derivatives (used interchangeably) as usedherein is to be broadly construed. In the first instance alkyl anddialkyl mono and diesters of oxalic acid are intended. The alkyl moietyof the esters generally have from about 1 to about 10 carbon atoms,preferably about 1 to 6 and most preferably about 1 to 4 carbon atoms.The alkyl moiety may be substituted, unsubstituted, cyclic, linear,branched or unbranched but is predominantly hydrocarbon in character.Oxalic acid derivatives, in one embodiment could include carboxylic acidderivatives other than esters, e.g., amides, acid halides, andanhydrides. Preferred oxalic acid derivative in the practice of thisinvention are the methyl and ethyl diesters of oxalic acid. Generally,the oxalic acid derivatives that can be used in the present invention,include oxalic acid derivatives for formula (I)

wherein R₁ and R₂ are independently hydroxyl, oxygen, a halide, asubstituted or unsubstituted amine, OR₃ or a side chain of formula (II):

wherein R₃ and R₄ are independently a branched or unbranched, cyclic orlinear, saturated or unsaturated, substituted or unsubstituted alkyl offrom 1 to 10 carbon atoms; and wherein R₁ and R₂ cannot both behydroxyl.

In general, prior to beginning the pretreatment process, the fibrouslignocellulose material is first reduced to a size appropriate forpulping. Methods of reducing fibrous lignocellulosic material toappropriate sizes for pulping are conventional in the art. Reducing thesize of the fibrous lignocellulose material aids in having the materialsufficiently treated with the oxalic acid or oxalic acid derivative. Inone embodiment, the material to be treated is reduced to wood chips.Generally acceptable size for wood chips include chips in a size rangeof 1 mm to 100 mm in length. It is anticipated, however, that thepresent method may also be effective with materials not reduced to woodchips, such as those materials derived from recovered paper or woodresidues or logs themselves. It is also anticipated that the presentmethod may be effective in treating pulp itself.

The reduced fibrous lignocelluosic material is then treated with anamount of oxalic acid or an oxalic acid derivative. The level of oxalicacid or oxalic acid derivative used is empirically derived for thespecies of wood and the end use of the fiber. Higher concentrations maybe used to recover hemicelluloses from wood chips destined for chemicalpulps or total saccharification (enzymatic or second acid hydrolysis)than can be used for those to be used for mechanical andthermomechanical pulps. Generally, the amount of oxalic acid or oxalicacid derivative employed, as expressed in dry weight percentage, may beless than about 6%, or suitably less than about 5%, or more suitablybetween about 0.05% and 5%, or even more suitably between about 1% and3%, of the dry weight of the fibrous lignocellulosic material.

In one embodiment, the method comprises adding oxalic acid,dimethyloxalate or diethyloxalate oxalic acid esters in the presence ofheated wood chips, pulp or any lignocellulosic source that has somewater of hydration. Suitably the wood chips are first heated in adigester, using direct atmospheric steam injection to exclude air fromthe digester and bring the chips up to a temperature required forreaction. The digester is then suitably brought up to around 30 psigsteam pressure (although 0 to 90 psig steam can be used) by acombination of steam injection and jacket pressure. This is continueduntil a stable temperature and pressure are obtained. The temperatureused is generally greater than 100° C., typically between 130° C. and140° C. No upper limit has been established and temperatures of 170° C.have been used to extract sugars.

Oxalic acid or oxalic acid derivatives of low volatility are suitablyapplied by impregnating the steamed wood chips with a liquid solution.Volatile oxalic acid derivatives such as dimethyloxalate ordiethyloxalate may alternatively be applied by injecting into thedigester by gas pressure, suitably using carbon dioxide or nitrogen.Generally, the pressure of the reaction increases slightly due to thevaporization of the chemical and diminishes within 2-3 minutes. Thediethyloxalate or dimethyloxalate oxalic acid esters rapidly vaporizeallowing for the delivery of the chemical into wood chips. The vaporizedchemical contacts water present within the wood chips and at least oneester hydrolyzes to liberate acid which acidifies the water. Since thewater is kept to a minimum the acid concentration is high andproportional to the amount of chemical injected. The elevatedtemperature and localized acidity combine to hydrolyze thehemicellulosic sugars present in the wood chips. Other reactions such asesterification and transesterification are also possible during thisincubation. The delivery of the reactants via the vapor phase provides ahigh concentration of acid at the water surface layer in the chips.

The oxalate ester will generate a vapor concentration of the chemicalthat is dependant on the volume of the vessel and amount of chemicalused. Increasing the concentration of the oxalate ester in the vesselwill increase the amount of carbohydrate liberated from a given weightof wood chips. A threshold value of oxalate ester has been observed,under a set time and temperature, in pine and spruce where the increasein sugars liberated decreases relative to the increase of oxalate esterused. This threshold value has not been observed for liberation ofhemicellulosic sugars from aspen and maple. In one embodiment, a rangeof 0 to 100 ml of oxalic acid or diethyl oxalate has been used for thetreatment of aspen, oak, maple, southern yellow pine, red pine andspruce in a reactor with a total volume of 21.4 liters. In thisembodiment, increasing the wood chips (from 1.25 kg to 2.5 kg oven drybasis) increased the amount of hemicellulosic sugars liberated from thewood chips.

Suitably, the treated wood chips are maintained at a steady temperaturefor a time period of between 5 minutes and 2 hours. Maintaining the woodchips in the digester for a more extended time will release morehemicellulosic sugars. Increasing the temperature of reaction orchemical loading will also release more hemicellulosic sugars. Atemperature systematically increasing and/or decreasing in time may alsobe employed.

Conventional hot water extraction may be used for hemicellulosic sugarextraction. Suitably, the wood chips may be heated to 170° C. for 30minutes with hot water at a water to wood ratio of 4:1. The water may becollected for extractives including the sugars, etc. for fermentation orother uses.

The extracted, washed wood chips arc then ready for pulping. Manypulping methods are suitable for the present invention includingmechanical and chemical pulping methods. Mechanical pulping methodsinclude mechanical pulping, thermo-mechanical pulping (TMP), chemicaltreatment with thermo-mechanical pulping (CTMP), and chemi-mechanicalpulping (CMP). Chemical pulping methods include chemical pulping,sulfate (kraft) and sulfite processes. Suitably, the wood chips are usedfor thermomechanical pulp generation. Thermomechanical pulp generationwith treated chips have been shown to provide energy savings from 25 to50%.

In one embodiment, when the treated wood chips are subjected tomechanical pulping, dilution water is added to the treated material andthe material is run through a mechanical refiner in a number ofsequential passes. The number of passes of the treated material/pulpmixture will depend upon the freeness desired for the particular MDF tobe made. The treated material/pulp mixture is repeatedly fed throughrefiners until the desired level of freeness is achieved. The pulp mayalso be dewatered as necessary between passes. Loblolly pine, treatedusing the procedures described above, requires between about 2 to 6repeated passes to obtain a 100 ml CSF value in a single rotating 300 mmdiameter disk atmospheric refiner.

The overall energy efficiency of the process can be compared with thatof a standard process by pulping untreated material in the sameapparatus while at the same time monitoring the energy consumption ofthe refining mill. Generally speaking the treated material requiressignificantly less energy input through the refiner to achieve the samelevel of freeness in the resulting pulps.

The pulps made through this procedure may then be made into MDF boardsusing standard techniques.

The present invention is further explained by the following exampleswhich should not be construed by way of limiting the scope of thepresent invention.

EXAMPLES Example 1

Properties of MDF made from wood pretreated with OA and DEO. Red pinelogs were obtained from SENA. Logs were debarked and chipped at FPL to anominal size of 6-14 mm. Chips were placed in barrels and frozen toprevent the growth of contaminating microorganisms. Their moisturecontent was 42%.

Processing of control chips. Untreated (control) red pine wood chipswere placed in a large rotating digester and steam was introduced todisplace air and bring the chips to temperature (135-140° C.). Externaltemperature measurement was used as well as an internal probe as asecondary source of temperature measurement. The chips were cooked for30 minutes at 135° C. Following the cook, the wood chips were subjectedto a sugar extraction procedure consisting of atmospheric hot waterwashing (˜240 liters, a water to wood ratio of 8:1) at a temperature of80° C. for 30 minutes to collect the extractives including the sugars,etc. for fermentation. The wood chips were then collected and stored at4° C. until TMP processing for MDF fiber.

Processing of Hot Water Chips. Untreated (control) red pine wood chipswere placed in a large rotating digester along with water (at a water towood ratio of 4:1). The temperature was raised to 170° C. and then heldat that temperature for 15 minutes. External temperature measurement wasused to monitor the temperature. Following the cook, the wood chips weresubjected to a sugar extraction procedure consisting of atmospheric hotwater washing (increasing the water volume to 240 liters, in a finalwater to wood ratio of 8:1) at a temperature of 80° C. for 30 minutes tocollect the extractives including the sugars, etc. for fermentation. Thewood chips were then collected and stored at 4° C. until TMP processingfor MDF fiber

Processing of oxalic acid (OA) treated chips. Oxalic acid dihydrate fromSigma-Aldrich was used in a quantity of 35 grams into 7500 ml. water at(0.33% wt. solution of oxalic acid) per 2.5-kilograms oven dried woodchips. Red pine wood chips were placed in a large rotating digester andsteam introduced to displace air and bring the chips to temperature(100° C.). The steam was stopped and a vacuum drawn on the digester andthe oxalic acid solution was admitted and allowed to impregnate thechips. The excess solution was drained and the temperature brought to135° C. When at temperature the chips were cooked for 10 minutes.Following the cook, the wood chips were subjected to a sugar extractionprocedure consisting of atmospheric hot water washing (˜240 liters, awater to wood ratio of 8:1) at a temperature of 80° C. for 30 minutes tocollect the extractives including the sugars, etc. for fermentation. Thewood chips were (hen collected and stored at 4° C. until TMP processingfor MDF fiber.

Processing of diethyloxalate (DEO) treated chips. Diethyloxalate fromSigma Aldrich was used in a quantity of 20-ml. per 1-kilogram oven driedwood chips. Red pine wood chips were placed in a large rotating digesterand steam introduced to displace air and bring the chips to temperature(140° C.). When at temperature the DEO was introduced by an injectorpipe attached to the top of the digester and forced into the digesterusing carbon dioxide or nitrogen gas pressure. External temperaturemeasurement and an internal temperature measurement probe were used.Chips were cooked for 30 minutes at 140° C. Following the cook, the woodchips were subjected to a sugar extraction procedure consisting ofatmospheric hot water washing (˜240 liters, a water to wood ratio of8:1) at a temperature of 80° C. for 30 minutes to collect theextractives including the sugars, etc. for fermentation. The wood chipswere then collected and stored at 4° C. until TMP processing for MDFfiber.

TMP Production. The cooked wood chips prepared as indicated above werefiberized in a Laboratory Pressurized Refiner (TMP). The TMP is a12-inch single disc pressurized mechanical Sprout-Bauer, model #12-1CP.Energy consumption was measured using an Ohio Semitronic Model WH30-11195 Integrating Wattmeter attached to the power supply side of the44.8 kW electric motor. The feed rate through the refiner was 1 kg/min.Energy was reported in W·h/kg. The refiner plate gap settings wereapproximately 0.005 inch.

MDF production. The fiberized wood as made into 19 mm thick panels, madeat 5% moisture content using a commercial phenol-formaldehyde resin.After preparation the boards were cut and physical properties of theboards determined using the standard testing techniques found in the(ASTM D 1037-78, 2005) American Society for Testing and Materials. 2005.Annual book of ASTM Standards. Vol. 04.10 Wood. ASTM International, WestConshohocken, Pa., which is incorporated by reference here in itsentirety. The study shows that hemicellulosic sugars can be removed andrecovered prior to MDF production and the MDF has enhanced propertiescompared to the control. The results for the study arc shown in Table 1.

TABLE 1 Water soak (24 hour) Carbohydrate Swell Absorption released, %or wood Wood treatment (%) (%) chip Control 9.1 30.6 1.1 Oxalic acid 4.016.0 4.4 DEO 3.8 13.5 5.3 Hot water 12.0 93.9 7.6 Table 1 Red pinemedium density fiberboard tests and extent of carbohydrate removal. MDFproperties from boards containing 93.5% fiber, 6% resin and 0.5% wax.

It was not evident that the samples would have increased waterrepellency as a result of the OA and DEO pretreatments and subsequentextraction. The normal extraction procedures that are done with hotwater have not been shown to have this benefit to the MDF production.

Example 2

Materials and Methods. Wood chips. Red pine logs were obtained fromSENA. Logs were debarked and chipped at FPL to a nominal size of 6-14mm. Chips were placed in barrels and frozen to prevent the growth ofcontaminating microorganisms. Moisture content was 42%. After theexperimental cooking procedures, the wood chips were collected andstored at 4° C. until TMP processing for MDF fiber.

Experimental cooks. Control red pine wood chips were subjected to timeand temperature and extraction protocols, but without chemical cook(positive control). Following the cook, the wood chips were subjected tothe extraction procedure consisting of atmospheric hot water washing(˜240 liters) to collect the extractives including the sugars, etc. forfermentation.

Oxalic acid dihydrate obtained from Sigma-Aldrich was used in a quantityof 35 grams into 7500 ml. water at 70° C. (0.33% solution of oxalicacid) per 2.5-kilograms oven dried wood chips. A rotating digester wasused to cook the wood chips to the desired temperature and time.External temperature measurement and an internal temperature measurementprobe were used. The chips were cooked for 10 minutes at 135° C.Following the cook, the wood chips were subjected to the extractionprocedure consisting of atmospheric hot water washing (˜240 liters) tocollect the extractives including the sugars, etc. for fermentation.

Diethyloxalate (DEO) obtained from Sigma Aldrich was used in a quantityof 20-ml. per 1-kilogram oven dried wood chips. A rotating digester wasused to cook the wood chips to the desired temperature and time.External temperature measurement and an internal temperature measurementprobe were used. Chips were cooked for 30 minutes at 135° C. Followingthe cook, the wood chips were subjected to the extraction procedureconsisting of atmospheric hot water washing (˜240 liters) to collect theextractives including the sugars, etc. for fermentation.

Pine wood chips were subjected to hot water extraction. The wood chipswere heated to 170° C. for 30 minutes with hot water, where the water towood ratio was 4:1. Following the cook, the water was collected forextractives including the sugars, etc. for fermentation.

Fiber production for the TMP process. Cooked wood chips were fiberizedin a Laboratory Pressurized Refiner (TMP). The TMP was a 12-inch singledisc pressurized mechanical Sprout-Bauer, Model #12-1CP. Energyconsumption was measured using an Ohio Semitronic Model WH 30-11195integrating a Wattmeter attached to the power supply side of the 44.8 kWelectric motor. Feed rate through the refiner was 1 kg/min. Energy isreported in W·h/kg. Refiner plate gap settings were approximately 0.005inch.

MDF production. 19 mm thick panels were made at 5% moisture contentusing a commercial phenol-formaldehyde resin. After preparation, theboards were cut and physical properties of the boards determined usingthe standard testing techniques found in ASTM D 1037-78, 2005. AmericanSociety for Testing and Materials (2005), Annual book of ASTM Standards,Vol. 04.10, Wood, ASTM International, West Conshohocken, Pa.

Results. After OA and DEO pretreatments, hemicellulosic sugars can beremoved and recovered prior to MDF production and the MDF has enhancedproperties compared to both the raw control and the hot water control.

TABLE 2 Red pine medium density, fiberboard tests and extent ofcarbohydrate removal. Bending Internal Water soak (24 hour) CarbohydrateWood MOR MOE bond Swell Absorption released % treatment (N/mm²) (N/mm²)(N/mm²) (%) (%) Wood chip Control 16.8 1824.9 0.179 9.1 30.6 1.1 Oxalicacid 14.3 1457.3 0.241 4.0 16.0 4.4 DEO 14.3 1498.5 0.193 3.8 13.5 5.3Hot water 16.2 1598.6 0.172 12.0 93.9 7.6 Note: MDF properties fromboards containing 93.5% fiber, 6% resin and 0.5% wax.

Unexpected superior results. It was not evident that the samples wouldhave increased water repellency as a result of the OA and DEOpretreatments and subsequent sugar extractions. The normal extractionprocedures that are done with hot water have not been shown to have thisbenefit to the MDF production. We were surprised to see this result.

Example 3

Pilot scale data were generated at the Andritz Research and DevelopmentLaboratory in Springfield, Ohio. The Andritz facility is known toprovide refining results similar to industrial scale such that dataobtained can be used for scaled up with confidence. The procedures usedto process both the red pine and the spruce wood used in the refiningtests at Andritz were the same procedures as described above formaterials and methods.

TABLE 3 Pilot-scale refining results from Andritz on spruce. BendingInternal Water soak (24 hour) Carbohydrate Wood MOR MOE bond SwellAbsorption released % treatment (N/mm²) (Nmm²) (N/mm²) (%) (%) Wood chipSpruce 13.5 1558 0.18 31.2 110.0 1.2 Control Spruce 14.8 1951 0.41 14.866.6 3.5 Oxalic Acid Spruce DEO 19.3 1951 0.44 10.0 32.1 4.0 Note: MDFproperties from boards containing 93.5% fiber, 6% resin and 0.5% wax.Carbohydrate is the total identified carbohydrate (mannose + xylose +arabinose + glucose + galactose, in decreasing order) released as apercentage of the weight of the wood chips.

TABLE 4 Pilot-scale refining results from Andritz on red pine. BendingInternal Water soak (24 hour) Carbohydrate Wood MOR MOE bond SwellAbsorption released % treatment (N/mm²) (N/mm²) (N/mm²) (%) (%) Woodchip Red Pine 19.3 2124 0.31 19.6 72.6 1.0 Control RedPine 15.4 15790.32 15.2 39.2 5.5 Oxalic Acid Note: MDF properties from boardscontaining 93.5% fiber, 6% resin and 0.5% wax. Carbohydrate is the totalidentified carbohydrate (mannose + xylose + arabinose + glucose +galactose, in decreasing order) released as a percentage of the weightof the wood chips.

For the treated red pine wood chips, the resulting MDF strength wasslightly lower than the control. However, the unexpected waterrepellency was evident. For the treated spruce wood chips, the waterrepellency was again unexpectedly increased over the control, and thestrength of the resulting MDF was also surprisingly enhanced. The redpine species in Table 4 was very similar to that shown in Table 2.

Utility of the Described Embodiments

MDF is widely used as a structural material in objects such as buildingsand furniture. In many of these uses the MDF may become exposed towater. It is well known that exposure to water causes deterioration ofconventionally-produced MDF, resulting in losses of mechanicalintegrity, dimensional stability, and asthetic appearance. Because ofthis it is common to restrict the use of MDF to applications free frommoisture exposure, and/or to apply protective paints, varnishes, orother coatings in an attempt to ameliorate the negative effects ofmoisture on the material. These applied coatings represent an additionalcost and may not be fully satisfactory for various uses.

Methods currently in use to improve the water repellency of MDF involvethe addition of water-repellent materials to the MDF. Additional bindingresin and/or specific water repellency materials can be added to theMDF. A useful and distinguishing feature of applicants' invention isthat additional water repellent materials need not be added to the MDF.This is because the improved water repellency is achieved through aninitial chemically-induced modification to the lignocellulosic materialitself before the MDF is formed. The modified lignocellulosic fibersremain compatible with the binding resin used to form the board.

While the present invention has now been described and exemplified withsome specificity, those skilled in the art will appreciate the variousmodifications, including variations, additions, and omissions that maybe made in what has been described. Accordingly, it is intended thatthese modifications also be encompassed by the present invention andthat the scope of the present invention be limited solely by thebroadest interpretation that lawfully can be accorded the appendedclaims.

1. A method of making Medium Density Fiberboard (MDF) having improvedmoisture tolerance comprising: providing a fibrous lignocellulosematerial; treating the material with a compound having the formula

wherein R₁ and R₂ are independently a member selected from the groupconsisting of —OH, halide, substituted amine, unsubstituted amine, —OR₃,and

wherein R₃ and R₄ are independently a branched or unbranched, cyclic orlinear, saturated or unsaturated, substituted or unsubstituted C₁₋₁₀alkyl, at a temperature in the range of 90-170° C. generating a treatedmaterial; extracting hemicellulose sugars from the treated material;refining the treated material to generate a fibrous pulp, wherein therefining step can be performed either before or after the extractionstep; adding a suitable resin to the fibrous pulp; and forming thefibrous pulp into medium density fiberboard.
 2. The method of claim 1,wherein the fibrous lignocellulose material is reduced to a particlesize in the range of 1-100 mm in length.
 3. The method of claim 2,wherein the reduced material is treated with less than 6 dry wt % of thecompound.
 4. The method of claim 2, wherein the reduced material istreated with 0.05-5 dry wt % of the compound.
 5. The method of claim 2,wherein the reduced material is treated with 1-3 dry wt % of thecompound.
 6. The method of any one of claims 2-5, wherein R₁ and R₂ are—OH.
 7. The method of any one of claims 2-5, wherein R₁ and R₂ are —OR₃,and wherein R₃ is an ethyl.
 8. The method of any one of claims 2-5,wherein R₁ and R₂ are —OR₃, and wherein R₃ is a methyl.
 9. The method ofclaim 2, wherein the reduced material is treated at a pressure less than90 psig.
 10. The method of claim 2, wherein the reduced material istreated for a duration less than 4 hours.
 11. The method of claim 2,wherein the reduced material is treated for a duration in the range of 5min. to 2 hours.
 12. The method of claim 2, wherein the reduced materialis treated at a temperature in the range of 130-140° C.
 13. The methodof claim 2, wherein the suitable resin is a phenol-formaldehyde resin,and wherein a wax is further added to the fibrous pulp.
 14. The methodof claim 13, wherein the medium density fiber board comprises 93.5 wt %fiber, 6 wt % resin, and 0.5% wax.
 15. The method of claim 2, whereinthe reduced material is refined by using a processing technique selectedfrom the group consisting of mechanical pulping, thermo-mechanicalpulping, and chemical treatment with mechanical pulping.
 16. The methodof claim 2, further comprising: mechanically refining the treatedreduced material one or more times to achieve a predetermined level offreeness of the treated reduced material; and dewatering the refined andtreated reduced-material one or more times.
 17. The method of claim 16,wherein the treated reduced material is mechanically refined 2-6 times,and wherein a freeness value of 100 ml CSF is achieved.
 18. The methodof claim 1, wherein the ratio of water:fibrous lignocellulose is in therange of 4:1 to 8:1.
 19. The method of claim 2, wherein the fibrouslignocellulose includes one or more members selected from the groupconsisting of southern yellow pine, red pine, spruce, western hemlock,aspen, loblolly pine and recovered paper.
 20. The method of claim 19,wherein the particle size is in the range of 6-14 mm in length.
 21. Themethod of claim 2, wherein the step of treating the reduced materialincludes cooking the material at a temperature in the range of 90-170°C.
 22. The method of claim 2, wherein the reduced material is furthertreated with one or more suitable enzymes and/or acetic acid.
 23. Themethod of claim 1, wherein the refining step can be performed eitherbefore or after the sugar extraction step.
 24. A medium density fiberboard made by any one of the methods of claims 2-5.
 25. A medium densityfiber board made by claim
 6. 26. A medium density fiber board made byclaim
 7. 27. A medium density fiber board made by claim
 8. 28. A mediumdensity fiber board made by any one of claims 9-23.